Nano-dispersed powders and methods for their manufacture

ABSTRACT

Dispersed powders are disclosed that comprise fine nanoscale powders dispersed on coarser carrier powders. The composition of the dispersed fine powders may be oxides, carbides, nitrides, borides, chalcogenides, metals, and alloys. Fine powders discussed are of sizes less than 100 microns, preferably less than 10 micron, more preferably less than 1 micron, and most preferably less than 100 nanometers. Methods for producing such powders in high volume, low-cost, and reproducible quality are also outlined. Such powders are useful in various applications such as catalysts, sensor, electronic, electrical, photonic, thermal, biomedical, piezo, magnetic, catalytic and electrochemical products.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates, in general, to nano-dispersedpowders, and, more particularly, to nano-dispersed, complex compositionfine powders and methods to produce such powders.

[0003] 2. Background of the Invention

[0004] Powders are used in numerous applications. They are the buildingblocks of catalytic, electronic, telecommunication, electrical,magnetic, structural, optical, biomedical, chemical, thermal andconsumer goods. On-going market demands for more efficient, reliable,smaller, faster, superior and more portable products have demandedminiaturization of numerous products. This, in turn, has demandedminiaturization of the building blocks, i.e. the powders. Sub-micron andnanoscale (or nanosize, ultra-fine) powders, with a size 10 to 100 timessmaller than conventional micron size powders, enable qualityimprovement and differentiation of product characteristics at scalescurrently unachievable by commercially available micron-sized powders.

[0005] Nanopowders in particular, and sub-micron powders in general, area novel family of materials whose distinguishing features include thattheir domain size is so small that size confinement effects become asignificant determinant of the materials' performance. Such confinementeffects can, therefore, lead to a wide range of commercially importantproperties. Nanopowders, therefore, are an extraordinary opportunity fordesign, development and commercialization of a wide range of devices andproducts for various applications. Furthermore, since they represent awhole new family of material precursors where conventional coarse-grainphysiochemical mechanisms are not applicable, these materials offerunique combination of properties that can enable novel andmultifunctional components of unmatched performance. Bickmore, et al. inU.S. Pat. No. 5,984,997, which along with the references containedtherein is incorporated herein by reference, teach some applications ofsub-micron and nanoscale powders.

[0006] Conventional dispersed powders comprise powders of a firstcomposition (e.g. metal) dispersed on the surface of a carrier which maybe of a second composition (e.g. carbon). The dispersed powder structureenables greater and more effective availability of the firstcomposition. It also provides a cost reduction because the secondcomposition can be a low-cost carrier. Additionally, the dispersedpowder structure improves the stability and enhances the performancesynergistically.

[0007] Dispersed powders are desired in a number of applications such ascatalysis. The junctions provide active sites for useful chemicalreactions. Dispersed powders are often produced using chemicalprecipitation techniques. These techniques fail to provide a fine anduniform distribution of the dispersed particles on the surfaces of thecarrier. Furthermore, the challenge becomes even more difficult whencomplex compositions need to be dispersed on a carrier powder. Chemicalprecipitation techniques also leave chemical residues on the surfacesthat sometimes are not desirable. Given the difficulty in theirproduction, few dispersed powders are known in the literature and thesehave found only limited applications.

[0008] Phillips in U.S. Pat. No. 5,989,648 (which, along with itsreferences, is specifically incorporated herein by reference) teaches aplasma-based method for preparing metal supported catalysts from anaerosol comprising a mixture of at least one metal powder and at leastone support powder. Phillips reports the unusual benefits as catalystsof the metal supported powders so prepared. However, Phillips does notoffer motivation for or methods of utilizing fluid precursors to formdispersed powders. Phillips also does not teach nano-dispersedsub-micron powders, motivations for their use, or their benefits tovarious applications.

SUMMARY OF THE INVENTION

[0009] Briefly stated, the present invention involves nano-dispersedpowders comprising powders that have been morphologically engineered.More specifically, the term nano-dispersed powders according to thisinvention refers to powders that have been arranged to provide a desiredmorphological distribution (dispersion) at nanoscale levels (e.g.,sub-100 nm levels). As described in the definition section,nano-dispersed powders comprise carrier particles and attached particlesdispersed on the surface of the carrier particles.

[0010] The carrier particles may be spherical, non-spherical, porous,tubular, planar, crystallites, amorphous, or any other useful form. Thenanoparticles may similarly be one-dimensional, two-dimensional, orthree-dimensional, spherical, non-spherical, porous, tubular, planar,crystallites, or amorphous forms, or any other useful form. The attachednano-dispersed particles may be free flowing, agglomerated, porous,coated, or hollow forms or any other useful form. The same carrier mayhave nanoparticles of more than one composition attached to its surface.In addition, various nano-dispersed particles of different compositionsmay be blended to achieve useful compositions.

[0011] The invention provides nano-dispersed powders with unusuallyengineered morphology. The unusual morphology provides a high density ofmulti-phasic points (i.e. points where two or more distinct phasesinteract with each other and/or species in the gas phase). Thesemorphologically engineered nano-dispersed powders offer benefits tonumerous applications. Some illustrative, but non-limiting applicationsinclude (a) catalytic transformation of less valuable chemicals andmaterial feed stocks into more valuable chemicals and materials; (b)catalytic transformation of more hazardous chemicals and materials intoless hazardous or non-hazardous forms of substances; (c) unusualphosphor, photonic, and optical materials for display, photonic, andoptical applications; (d) unusual carriers, tracers, drug deliveryvehicles, and markers for biomedical and genomic applications; (e)unusual building blocks for batteries, sensors, and electrochemicalproducts; (f) fillers for polymers, ceramics, and metal matrixcomposites; and (g) dopants for electronic, magnetic, thermal, piezo,electrical, tooling, structural, inks, paints, and topical healthproducts.

[0012] The concept of dispersed powders disclosed and their methods ofmanufacture may be applied to produce commercially useful submicron andmicron dispersed powders as well.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013]FIG. 1 shows an example of a sub-micron powder comprisingnanopowders discretely dispersed on and attached to the surface of thesubmicron powder.

[0014]FIG. 2 shows an example of a nanotube carrier having nanoparticlesdispersed on and attached to its surface, wherein at least two of thenanoparticles are not in contact with each other.

[0015]FIG. 3 shows one embodiment for producing nano-dispersed powdersby combining a metal precursor and carrier particles.

[0016]FIG. 4 shows a schematic concentric flame approach to improve theuniformity of particle size distribution.

[0017]FIG. 5 shows an alternate embodiment for producing nano-dispersedparticles in which both the nano-sized powders and the carrier particlesare prepared in-situ during the thermal processing.

[0018]FIG. 6 shows an alternate embodiment for producing nano-dispersedpowders by combining a metal precursor and carrier particles.

[0019]FIG. 7 shows an alternate embodiment for producing nano-dispersedpowders by combining a metal precursor and carrier particles.

[0020]FIG. 8 shows an alternate embodiment for producing nano-dispersedpowders by combining a metal precursor and carrier particles.

DETAILED DESCRIPTION OF THE INVENTION

[0021] The present invention is directed to dispersed powders in generaland dispersed nanoscale powders in particular. In a broad sense,dispersed powders provide a structure having a particle size that islargely determined by the size of a carrier particle, and surfacebehavior that is largely determined by dispersed particles attached tothe carrier particle. This somewhat oversimplifies dispersed particlestructures in that both the size and ultimate surface behavior may beaffected by each component, however the simplification is useful forunderstanding. With respect to dispersed nanoscale powders inparticular, the composite structure can be engineered to have somebenefits (e.g., cost, material handling, and the like) associated withlarger particle sizes while exhibiting behaviors, particularlysurface-related behaviors, of the nanoscale powders dispersed on thecarrier.

[0022]FIGS. 1 and 2 show two non-limiting examples of nano-dispersedsub-micron powders and nano-dispersed nanopowders, respectively. Forexample, FIG. 1 shows an example of a sub-micron powder comprisingnanopowders 200 discretely dispersed on and attached to the surface of asubmicron carrier 102. By “discretely” it is meant that the particles200 do not touch or overlap. In one sense means particles do notphysically overlap. In another sense means that they are sufficientlyseparate that the solid states of atoms within adjacent particles 200have a level of interaction determined by their separation. FIG. 2 showsan example of a nanotube carrier 203 having nanoparticles 200 dispersedon and attached to its surface, wherein at least two of thenanoparticles are not in contact with each other.

DEFINITIONS

[0023] Certain terms used to describe the invention herein are definedas follows:

[0024] “Fine powders” as used herein, refers to powders thatsimultaneously satisfy the following criteria:

[0025] (1) particles with mean size less than 100 microns, preferablyless than 10 microns; and

[0026] (2) particles with aspect ratio between 1 and 1,000,000.

[0027] “Submicron powders” as used herein, refers to fine powders thatsimultaneously satisfy the following criteria:

[0028] (1)particles with mean size less than 1 micron; and

[0029] (2)particles with aspect ratio between 1 and 1,000,000.

[0030] The terms “dispersed powders,” “morphologically-engineeredpowders,” “decorated powders,” and “surface dispersed powders” are usedinterchangeably and refer to powders that simultaneously satisfy thefollowing criteria:

[0031] (1) they comprise at least a first composition that serves as acarrier particle;

[0032] (2) they comprise particles of at least a second composition thatare attached to the surface of the carrier particle in a mechanicallystable state, where the second composition can be the same as ordifferent from the first composition;

[0033] (3) the surfaces of the attached particle and carrier particleinteract physically, chemically, or electrochemically, but the attachedparticles exhibit properties that are distinct from the carrierparticles;

[0034] (4) at least two neighboring attached particles on the surface ofthe carrier are not in contact with each other at ambient temperature(300 K);

[0035] (5) the average separation distance between the center of gravityof the at least two neighboring attached particles on the surface of thecarrier that are not in contact with each other is at least 1.05 timesthe average diameter of the attached particles, preferably greater than2.5 times the average diameter of the attached particles, morepreferably greater than 5 times the average diameter of the attachedparticles, and most preferably greater than 10 times the averagediameter of the attached particles; and (6) the attached particle issmaller than the carrier particle. More particularly, the ratio of theaverage diameter of the carrier particles and the average diameter ofthe attached particles is greater than or equal to 2, preferably greaterthan 10, more preferably greater than 25, and most preferably greaterthan 100. In one embodiment, the carrier powder is less than 1000microns, preferably less than 100 microns, more preferably 10 microns,and most preferably 1 micron.

[0036] The terms “nanopowders,” “nanosize powders,” and “nanoscalepowders” are used interchangeably and refer to fine powders thatsimultaneously satisfy the following criteria:

[0037] (1) particles having a mean size less than 250 nanometers,preferably less than 100 nanometers; and

[0038] (2) particles with an aspect ratio between 1 and 1,000,000.

[0039] “Pure powders” as used herein, refers to powders that have acomposition purity of at least 99.9%, preferably 99.99% by metal basis.

[0040] “Nano-dispersed powders” as used herein refers to dispersedpowders in which the attached particle is a nanopowder.

[0041] “Nano-dispersed sub-micron powders” as used herein refers todispersed powders in which the attached particle is a nanopowder and thecarrier particle is a sub-micron powder.

[0042] “Nano-dispersed nanopowders” as used herein refers to dispersedpowders where the attached particle is a nanopowder and the carrierparticle is also a nanoscale powder.

[0043] The terms “powder,” “particle,” and “grain” are usedinterchangeably and encompass oxides, carbides, nitrides, borides,chalcogenides, halides, metals, intermetallics, ceramics, polymers,alloys, and combinations thereof. The term includes single metal,multi-metal, and complex compositions. These terms further includehollow, dense, porous, semi-porous, coated, uncoated, layered,laminated, simple, complex, dendritic, inorganic, organic, elemental,non-elemental, composite, doped, undoped, spherical, non-spherical,surface functionalized, surface non-functionalized, stoichiometric, andnon-stoichiometric forms or substances. Further, the term powder in itsgeneric sense includes one-dimensional materials (fibers, tubes),two-dimensional materials (platelets, films, laminates, planar), andthree-dimensional materials (spheres, cones, ovals, cylindrical, cubes,monoclinic, parallelolipids, dumbbells, hexagonal, truncateddodecahedron, irregular shaped structures, etc.).

[0044] The term “aspect ratio” refers to the ratio of the maximum to theminimum dimension of a particle.

[0045] The definitions provided above are intended to be applied in theinterpretation and understanding of the present invention, and are notnecessarily applicable to interpretation of prior art and conventionalprocesses. Some inventive features of the present invention areimplicitly expressed in the definitions provided above, and are not tobe interpreted as admissions that the defined term is prior art. To theextent these definitions are inconsistent with or more specific than asimilar term used in the prior art, it is to be understood that thedefinition provided herein is preferred in the interpretation of theinvention.

[0046] The present invention is directed to dispersed powders in generaland dispersed nanoscale powders in particular. Dispersed powderspreferably simultaneously satisfy the following criteria:

[0047] (1) they comprise a carrier particle with at least a firstcomposition;

[0048] (2) they comprise particles of at least a second composition thatare dispersed on and attached to the surface of the carrier particle ina mechanically stable state (i.e., sufficiently attached to preventundesired physical mobility during normal use), where the composition ofthe attached particles may be the same as or different than the carrierparticle;

[0049] (3) the surfaces of the attached particle and carrier particleinteract physically, chemically, or electrochemically with each other,but the attached particles exhibit properties (e.g., electricalproperties, chemical properties, solid state properties,size-confinement properties, surface properties and/or the like) thatare distinct from the carrier particle;

[0050] (4) at least two neighboring attached particles on the surface ofthe carrier are not in contact with each other at ambient temperature(300 Kelvin);

[0051] (5) the average separation distance between the center of gravityof the at least two neighboring attached particles that are not incontact with each other is at least 1.05 times the average diameter ofthe attached particles, preferably greater than 2.5 times the averagediameter of the attached particles, more preferably greater than 5 timesthe average diameter of the attached particles, and most preferablygreater than 10 times the average diameter of the attached particles;and

[0052] (6) the attached particle is smaller than the carrier particle.More particularly, the ratio of the average diameter of the carrierparticles and the average diameter of the attached particles is greaterthan or equal to 2, preferably greater than 10, more preferably greaterthan 25, and most preferably greater than 100.

[0053] In one embodiment, the carrier particle is a ceramic composition(oxide, carbide, nitride, boride, chalcogenide) or an intermetalliccomposition (aluminide, silicide) or an elemental composition. Examplesof ceramic composition include, but are not limited to (a) simple oxidessuch as aluminum oxide, silicon oxide, zirconium oxide, cerium oxide,yttrium oxide, bismuth oxide, titanium oxide, iron oxide, nickel oxide,zinc oxide, molybdenum oxide, manganese oxide, magnesium oxide, calciumoxide, and tin oxide; (b) multi-metal oxides such as aluminum siliconoxide, copper zinc oxide, nickel iron oxide, magnesium aluminum oxide,calcium aluminum oxide, calcium aluminum silicon oxide, indium tinoxide, yttrium zirconium oxide, calcium cerium oxide, scandium yttriumzirconium oxide, barium titanium oxide, barium iron oxide and silvercopper zinc oxide; (c) doped oxides such as zirconium doped ceriumoxide, antimony doped tin oxide, boron doped aluminum oxide, phosphorusdoped silicon oxide, and nickel doped iron oxide; (d) carbides such assilicon carbide, boron carbide, iron carbide, titanium carbide,zirconium carbide, hafnium carbide, molybdenum carbide, and vanadiumcarbide; (e) nitrides such as silicon nitride, boron nitride, ironnitride, titanium nitride, zirconium nitride, hafnium nitride,molybdenum nitride, and vanadium nitride; (f) borides such as siliconboride, iron boride, titanium diboride, zirconium boride, hafniumboride, molybdenum boride, and vanadium boride; (g) complex ceramicssuch as titanium carbonitride, titanium silicon carbide, zirconiumcarbonitride, zirconium carboxide, titanium oxynitride, molybdenumoxynitride, and molybdenum carbonitride; and (h) non-stoichiometricceramics. Other preferred specifications for the carrier particles areprovided in Table 1. TABLE 1 Specifications for the carrier particlesParameter Desired Range Preferred Range Average particle 5 nm-5 mm 50nm-5 microns size Standard deviation 1 nm-10 micron  1 nm-1000 nm of theSize distribution Purity, by wt % Dependant on the >99.99% needs of theapplication and cost (normally, greater than 90%) Surface Area >1m²/gm >10 m²/gm XRD crystallite Amorphous, 1 nm to <1000 nm size >1micron Porosity Dependant on the High needs of the application and costComposition Ceramics, Single metal and elements, alloys multi-metaloxide ceramics

[0054] Preferably, the dispersed particles that are attached to thecarrier particle are elemental, ceramic, intermetallic or polymercompositions. The composition of the attached particles can be the sameas or different than the composition of the carrier particle. Theparticles are preferably separated from each other either uniformly ornon-uniformly across the surface of the carrier particle. In aparticular example, the distance between two neighboring attachedparticles on the surface of the carrier that do not touch each other isat least 2 Angstroms, but may be greater than 5 Angstroms, 10 Angstroms,50 Angstroms or more to meet the needs of a particular application.

[0055] Examples of elemental compositions for the dispersed, attachedparticles include, but are not limited to, (a) precious metals such asplatinum, palladium, gold, silver, rhodium, ruthenium and their alloys;(b) base and rare earth metals such as iron, nickel, manganese, cobalt,aluminum, copper, zinc, titanium, samarium, cerium, europium, erbium,and neodymium; (c) semi-metals such as boron, silicon, tin, indium,selenium, tellurium, and bismuth; (d) non-metals such as carbon,phosphorus, and halogens; (e) clusters such as fullerenes (C₆₀, C₇₀,C₈₂), silicon clusters, and nanotubes of various compositions; and (f)alloys such as steel, shape memory alloys, aluminum alloys, manganesealloys, and superplastic alloys.

[0056] Examples of ceramic compositions for the dispersed, attachedparticles include, but are not limited to, (a) simple oxides such asaluminum oxide, silicon oxide, zirconium oxide, cerium oxide, yttriumoxide, bismuth oxide, titanium oxide, iron oxide, nickel oxide, zincoxide, molybdenum oxide, manganese oxide, magnesium oxide, calciumoxide, and tin oxide; (b) multi-metal oxides such as aluminum siliconoxide, copper zinc oxide, nickel iron oxide, magnesium aluminum oxide,calcium aluminum oxide, calcium aluminum silicon oxide, indium tinoxide, yttrium zirconium oxide, calcium cerium oxide, scandium yttriumzirconium oxide, barium titanium oxide, and silver copper zinc oxide;(c) doped oxides such as zirconium doped cerium oxide, antimony dopedtin oxide, boron doped aluminum oxide, phosphorus doped silicon oxide,and nickel doped iron oxide; (d) carbides such as silicon carbide, boroncarbide, iron carbide, titanium carbide, zirconium carbide, hafniumcarbide, molybdenum carbide, and vanadium carbide; (e) nitrides such assilicon nitride, boron nitride, iron nitride, titanium nitride,zirconium nitride, hafnium nitride, molybdenum nitride, and vanadiumnitride; (f) borides such as silicon boride, iron boride, titaniumdiboride, zirconium boride, hafnium boride, molybdenum boride, andvanadium boride; (g) complex ceramics such as titanium carbonitride,titanium silicon carbide, zirconium carbonitride, zirconium carboxide,titanium oxynitride, molybdenum oxynitride, and molybdenum carbonitride;and (h) non-stoichiometric ceramics.

[0057] The nano-dispersed powders of this invention may further comprisecarrier particles having dispersed particles of more than onecomposition dispersed on and attached to their surfaces. In addition,the dispersed powders may comprise multiple layers of the attachedparticles, where the layers may be concentric or non-concentric. Otherpreferred specifications for the carrier particles are provided in Table2. TABLE 2 Specifications for dispersed, attached particles ParameterDesired Range Preferred Range Average particle Less than 5 micron 1nm-250 nm size Standard deviation 1 nm-750 nm 1 nm-50 nm of the Sizedistribution Purity, by wt % Dependent on the >99.99% needs of theapplication and cost (normally, greater than 90%) Surface Area >1m²/gm >100 m²/gm XRD crystallite Amorphous, 1 nm to <250 nm size 1micron Mechanical Dependant on the High Stability needs of theapplication and cost

[0058] The distinctive features that make nano-dispersed powders of thisinvention commercially desirable result in part from (a) the separationbetween the attached nanoparticles during their use, (b) the unusualproperties of attached nanoparticles, (c) the useful interaction betweenthe carrier composition and the dispersed attached particles, and (d)the morphologically induced interaction of dispersed attached particleinterfaces and the carrier particle interface with the chemical,electromagnetic, electrochemical, photonic, magnetic, charges, andthermodynamic environment around the dispersed particles.

[0059] More specifically, the distinct usefulness of nano-dispersedpowders is in part a result of the separation between the dispersednanoparticles attached to the surface of the carrier particle, which inturn reduces the potential sintering of the particles at highertemperatures. It is known in the art that closely packed small particlesin general, and nanoscale particles in particular, sinter faster as thetemperature of use increases. This limits the time during which theuseful performance of the particle is available. Many applications,particularly those that operate at high temperatures (e.g. catalysis),require that the surface and bulk properties of the material in use donot vary or that they vary only slightly with time. This is difficult toaccomplish with closely packed nanoparticles, because such nanoparticlessinter (diffuse and grow) across the grain boundaries as a function oftemperature and time. By dispersing the nanoparticles on the surface ofthe carrier particle, the surfaces of the dispersed nanoparticles arekept from touching each other. This reduces or eliminates theinteraction and consequent sintering between the nanoparticles, even athigh temperatures. As a result, the interaction at the grain boundary iseliminated, and consequently the time and temperature based variancesare eliminated. Thus, dispersing the nanoparticles solves an outstandingproblem that confronts attempts to utilize the beneficial properties ofnanoscale powders.

[0060] The distinct usefulness of nano-dispersed powders is also in parta result of the unusual inherent properties of nano-scaled particles.Nano-scaled materials are a family of materials whose distinguishingfeature is that their mean grain size is less than 100 nm. Nanopowders,because of their nanoscale dimensions (near-molecular), feature avariety of confinement effects that significantly modify the propertiesof the material. The physics behind this has been aptly conjectured tobe the following: a property will be altered when the entity ormechanism responsible for that property is confined within a spacesmaller than the critical length associated with that entity ormechanism. Such confinement effects lead to very desirable properties.For example:

[0061] (a) nanopowders have a very high surface area which leads toenhanced interfacial diffusivities and thus enables rapid, lowtemperature formation of materials that are typically difficult toprocess;

[0062] (b)nanopowders are isomorphic because of dimensional confinement.Furthermore, enhanced solubilities are observed leading tonon-equilibrium compositions. This leads to catalysts and reactants withextremely high surface areas, high selectivity and activity;

[0063] (c)nanopowders have grain sizes that are too small for Frank-Readdislocation to operate in the conventional yield stress domain;consequently, enhancement in strengths and hardness of 100% to 500% areobserved in films and pellets made from nanopowders;

[0064] (d)the size of the nanopowder is less than the wavelength ofvisible light; consequently unique optical materials with grain sizestailored for excitonic interactions with particular wavelengths can beprepared;

[0065] (e)nanopowders are confined to a dimension less than the meanfree path of electrons; consequently, unusual electrical andelectrochemical properties can be observed;

[0066] (f)nanopowders are confined to dimension less than the domainsize of magnetic materials; consequently, nanopowders are precursors tomagnetic materials exhibiting Giant Magnetoresistive (GMR) andsuperparamagnetic effects; and

[0067] (g) nanopowders feature quantum confinement to dimensions lessthan Debye length. This leads to electrochemical properties with orderof magnitude higher sensitivities to chemical species.

[0068] Nanopowders in general, and nano-dispersed powders in particular,thus provide an extraordinary opportunity for design, development andcommercialization of a wide range of structural, electrochemical,electrical, optical, electronic, magnetic and chemical applications.Furthermore, since nanopowders represent a whole new family of materialprecursors for which conventional coarse-grain physiochemical mechanismsare not performance determining, nanomaterials in general andnano-dispersed powders in particular offer unique combination ofproperties that can enable novel and multifunctional components ofunmatched performance.

[0069] Yet another source of distinct usefulness of nano-dispersedpowders results in part from the useful interaction between thedispersed attached nanoparticles and the carrier particles.Dimensionally confined nanomaterials have properties that are determinedin part by the interface thermodynamics and characteristics. Theseinterfaces in turn are influenced by neighboring atoms. By dispersion,the nanoparticles interact with the interface of the carrier particles.This interaction can induce a novel performance that is not exhibited byeither of the carrier particle or nanoparticle materials in isolation.

[0070] Yet another source of distinct usefulness of nano-dispersedpowders results in part from the high concentration of triple points.Triple points are the points where three or more phases meet and lead touseful interaction between the dispersed particles, the carrierparticles, and the fluid environment around the junction of dispersedand carrier particles. The nanoscale size of dispersed particlessignificantly increases the density of triple points. These are pointswhere useful chemical, electrochemical, physical, electronic, photonicand electrical interactions can occur.

[0071] 1. Methods of Producing Nano-Dispersed Powders

[0072]FIG. 3 shows one embodiment of a system for producing dispersedpowders in accordance with the present invention. This method can beused to produce dispersed powders that are coarse and pure, but isparticularly useful for nano-dispersed sub-micron and nano-dispersednanoscale powders.

[0073] The process shown in FIG. 3 begins at 100 with a metal-containingprecursor such as an emulsion, fluid, particle-containing liquid slurry,or water-soluble salt. The precursor may be a gas, a single-phaseliquid, a multi-phase liquid, a melt, fluid mixtures, or combinationsthereof. The metal-containing precursor comprise a stoichiometric or anon-stoichiometric metal composition wherein at least some portion is ina fluid phase. Fluid precursors are preferred in this invention oversolid precursors because fluids are easier to convey, evaporate, andthermally process, and the resulting product is more uniform.

[0074] In one embodiment of this invention, the precursors arepreferably environmentally benign, safe, readily available, high-metalloading, lower cost fluid materials. Examples of metal-containingprecursors suitable for purposes of this invention include, but are notlimited to, metal acetates, metal carboxylates, metal ethanoates, metalalkoxides, metal octoates, metal chelates, metallo-organic compounds,metal halides, metal azides, metal nitrates, metal sulfates, metalhydroxides, metal salts soluble in organics or water, andmetal-containing emulsions.

[0075] In another embodiment, multiple metal precursors may be mixed ifcomplex nano-dispersed powders are desired. For example, a bariumprecursor and iron precursor may be mixed to prepare high purity bariumferrite powders. As another example, a yttrium precursor, bariumprecursor, and copper precursor may be mixed in correct proportions toyield a high purity YBCO powder for superconducting applications. In yetanother example, an aluminum precursor and silica precursor may be mixedto yield aluminum silicate powders. Such complex nano-dispersed powderscan help create materials with surprising and unusual properties notavailable through the respective single metal oxides or a simplenanocomposite formed by physical blending powders of differentcompositions. To illustrate, nanoscale powders formed from blending twoor more metals can create materials with a hardness, refractive index,or other property or a combination of such properties that have valuesthat are intermediate to the properties of the respective single metaloxide forms. As an example, complex powders may be prepared fromaluminum and silicon precursors to create novel aluminum silicatenanomaterials with refractive index that is intermediate to therefractive index of the alumina and silica.

[0076] In all embodiments of this invention, it is desirable to useprecursors of a higher purity to produce a nano-dispersed powder of adesired purity. For example, if purities greater than x % (by metalbasis) is desired, one or more precursors that are mixed and used havepurities greater than or equal to x % (by metal basis) to practice theteachings herein.

[0077] With continued reference to FIG. 3, the metal-containingprecursor 100 (containing one or a mixture of metal-containingprecursors) is mixed with carrier particles 102 of desired size,composition, and characteristics. Carrier particles 102 may comprisemicron-sized particles, sub-micron particles, or nanostructuredparticles. The resultant slurry precursor 104 is the preferred feedmaterial for producing nano-dispersed powders. The relativeconcentrations of the metal-containing precursors 100 and the carrierparticles 102 should be substantially equivalent to that desired in thefinal product.

[0078] Upon formation of the slurry precursor 104, the slurry precursor104 is fed into a high temperature process 106 implemented using a hightemperature reactor, for example. In one embodiment, a synthetic aidsuch as a reactive fluid 108 can be added along with the slurryprecursor 104 as it is being fed into the reactor 106. For example, whenthe object is to prepare a nano-dispersed powder comprising a dispersedoxide, a preferred embodiment of this invention is to use a precursor100 in which the oxygen-to-carbon elemental ratio in the precursormolecule is high. Alternatively, or in addition, a reactive fluid 108that provides excess oxygen may be added along with the slurry precursor104 to the reaction zone 106. Examples of such reactive fluids include,but are not limited to, oxygen gas and air.

[0079] As another example, when the object is to prepare anano-dispersed powder comprising a dispersed carbide, a preferredembodiment of this invention is to use a precursor 100 in which theoxygen-to-carbon elemental ratio is less than 0.1, more preferably lessthan 1.0, and most preferably less than 2.0. Alternatively, or inaddition, a reactive fluid 108 that provides excess carbon or reducesexcess oxygen may be added along with the slurry precursor 104 to thereaction zone 106. Examples of such reactive fluids include, but are notlimited to, methane, ethylene, acetylene, ethane, natural gas, benzene,naphtha, and hydrogen.

[0080] As another example, when the object is to prepare anano-dispersed powder comprising a dispersed nitride, a preferredembodiment of this invention is to use a precursor 100 in which theoxygen-to-nitrogen elemental ratio in the precursor molecule less than0.1, more preferably less than 1.0, and most preferably less than 2.0.Alternatively, or in addition, a reactive fluid 108 that provides excessnitrogen or reduces excess oxygen may be added along with the slurryprecursor 104 to the reaction zone 106. Examples of such reactive fluidsinclude, but are not limited to, amines, ammonia, hydrazine, nitrogen,and hydrogen.

[0081] As another example, when the object is to prepare anano-dispersed powder comprising a dispersed boride, a preferredembodiment of this invention is to use a precursor 100 in which theoxygen-to-boron elemental ratio in the precursor molecule less than 0.1and more preferably less than 1.0, and most preferably less than 1.5.Alternatively, or in addition, a reactive fluid 108 that provides excessboron or reduces excess oxygen may be added along with the slurryprecursor 104 to the reaction zone 106. Examples include, but are notlimited to, boranes, boron, and hydrogen.

[0082] As another example, when the object is to prepare anano-dispersed powder comprising a dispersed carbonitride, a preferredembodiment of this invention is to use a precursor 100 in which the (a)oxygen-to-carbon elemental ratio in the precursor molecule less than 0.1and more preferably less than 1.0, and most preferably less than 2.0,and (b) the oxygen-to-nitrogen elemental ratio in the precursor moleculeless than 0.1, more preferably less than 1.0, and most preferably lessthan 2.0. Alternatively, or in addition, a reactive fluid 108 may beadded along with the slurry precursor 104 to the reaction zone 106.Examples of such reactive fluids include, but are not limited to,methane, ethylene, acetylene, ethane, natural gas, benzene, naphtha,amines, ammonia, hydrazine, nitrogen, and hydrogen.

[0083] While the above examples specifically teach methods of preparingdispersed powders of oxides, carbides, nitrides, borides, andcarbonitrides, the teachings may be readily extended in an analogousmanner to other compositions such as chalcogenides. While it ispreferred to use high temperature processing, a moderate temperatureprocessing or a low/cryogenic temperature processing may also beemployed to produce high purity nano-dispersed powders.

[0084] The precursor 100 may be also pre-processed in a number of otherways before the high temperature thermal treatment. For example, the pHmay be adjusted to ensure stable precursor. Alternatively, selectivesolution chemistry such as precipitation may be employed to form a solor other state of matter. The precursor 101 may be pre-heated orpartially combusted before the thermal treatment.

[0085] The slurry precursor 104 may be injected axially, radially,tangentially, or at any other angle into the high temperature region106. As stated above, the slurry precursor 104 may be pre-mixed ordiffusionally mixed with other reactants. The slurry precursor 104 maybe fed into the thermal processing reactor by a laminar, parabolic,turbulent, pulsating, sheared, or cyclonic flow pattern, or by any otherflow pattern. In addition, one or more metal-containing precursors 100can be injected from one or more ports in the reactor 106. The feedspray system may yield a feed pattern that envelops the heat source or,alternatively, the heat sources may envelop the feed, or alternatively,various combinations of this may be employed. A preferred embodiment isto atomize and spray the feed in a manner that enhances heat transferefficiency, mass transfer efficiency, momentum transfer efficiency, andreaction efficiency. The reactor shape may be cylindrical, spherical,conical, or any other shape. Methods and equipment such as those taughtin U.S. Pat. Nos. 5,788,738, 5,851,507, and 5,984,997 (each of which isspecifically incorporated herein by reference) can be employed inpracticing the methods of this invention.

[0086] With continued reference to FIG. 3, after the slurry precursor104 has been fed into reactor 106, it is processed at high temperaturesto form the product nano-dispersed powder. The thermal treatment ispreferably done in a gas environment with the aim to produce a productsuch as powders that have the desired porosity, strength, morphology,dispersion, surface area, and composition. This step producesby-products such as gases. To reduce costs, these gases may be recycled,mass/heat integrated, or used to prepare the pure gas stream desired bythe process.

[0087] The high temperature processing is conducted at step 106 (FIG. 3)at temperatures greater than 1500° C., preferably 2500° C., morepreferably greater than 3000° C., and most preferably greater than 4000°C. Such temperatures may be achieved by various methods including, butnot limited to, plasma processes, combustion, pyrolysis, electricalarcing in an appropriate reactor, and combinations thereof. The plasmamay provide reaction gases or just provide a clean source of heat.

[0088] An outstanding problem with conventional nanopowder synthesismethods is broad size distribution. This may happen because ofnon-uniformities in heat, mass, and/or momentum transfer. One reason forsuch non-uniformities is the sudden drop in temperature and reactingspecies at the outer edge of the reaction front such as a combustionflame. An illustration of outer edge of a flame would be the outerperimeter of the cross section of the flame, i.e. plane perpendicular tothe direction of flame flow. At these edges, the reaction pathways areinfluenced by the heat and mass and momentum boundary conditions. Thiszone, therefore, yields conditions where the product produced isnon-uniform and therefore different than those produced inside theboundary. Such conditions apply to all sorts of high temperature flowfields including flames and are created by various types of burners orreactor system. Some illustrations of such burners are taught by R. M.Fristrom (in Flame Structure and Processes, Oxford University Press, NewYork, 1995, which along with references contained therein isspecifically incorporated herein by reference).

[0089] One feature of this invention is the ability to reduce thisnon-uniformity by eliminating or reducing the above-described source ofnon-uniformity. This can be accomplished in many ways. As anillustration, the reaction zone (such as a combustion flame) can besurrounded by a fully or a partially concentric zone of a medium with athermal, mass and momentum profile that reduces such non-uniformity. Forexample, FIG. 4 shows a primary combustion burner 420, over which usefulparticle producing flame chemistry occurs, is preferably surrounded by aconcentric secondary burner 421 where a fuel is burned to maintain theouter edge temperatures in region 422 as close to the primary flame'shighest temperature in region 423 as possible. To the extent possible,the mass and momentum profile of the medium created by the concentricsecondary burner 421 should be similar in one or more respects to themass and momentum profile of the medium created by the primary burner420. Such concentric burners can assist in a more uniform thermal, mass,and momentum profile for the reaction space created by the primaryburner 420. A non-limiting illustration of such concentric burners isdiscussed and referenced by Howard et al., Carbon 30(8):1183-1201(1992), which along with references contained therein is specificallyincorporated herein by reference.

[0090] In another embodiment the slurry precursor 104 is pre-treated tominimize non-uniformity in heat, mass, and/or momentum transfer. Thiscan be achieved through techniques such as (a) axially, radially, ortangentially surrounding the high temperature processing zone 106 withan inert gas plasma, (b) axially, radially, or tangentially surroundingthe high temperature processing zone 106 with a complete combustionflame, preferably of high temperature, or (c) axially, radially, ortangentially surrounding the high temperature processing zone 106 withan electrical arc or high temperature radiation source. The concentricflame's adiabatic temperature (or concentric thermal zone) is preferablygreater than 500° C., more preferably greater than 1000° C., and mostpreferably greater than 2000° C. The minimal requirement of thistechnique is that the high temperature processing zone temperature atthe outer edges be higher when the concentric high temperature thermalzone is present than when it is absent.

[0091] This principle of concentric thermal zones can be applied to anymethod of producing dispersed powders. Illustrative examples ofprocesses where this principle can be used include one-dimensionalcombustion flames, diffusion flames, turbulent flames, pre-mixed flames,flat flames, plasma, arcing, microwave, sputtering, pyrolysis, sprayevaporation, laser and hydrothermal processing.

[0092] In the embodiment shown in FIG. 3, carrier particles 102 arepresent in the high temperature process. The carrier particles 102 maybe substantially inert during high temperature process 106, or they maybe transformed by physical, chemical, or solid state reactions. Hightemperature processing is performed in a manner such that the endproduct of high temperature process 106 includes carrier particles 102of desired size, composition and uniformity. Alternatively, the carrierparticles can be added at a later stage of the high temperature process.

[0093] The high temperature process 106 results in a vapor comprisingfine powders and carrier particles. After the thermal processing, thisvapor is cooled at step 110 to nucleate dispersion of fine powders,preferably nanopowders, onto the surface of the carrier particles.Preferably, the cooling temperature at step 110 is high enough toprevent moisture condensation. The dispersed particles are formed fromthe precursor because of the thermokinetic conditions in the process. Byengineering the process conditions such as pressure, residence time,flow rates, species concentrations, diluent addition, degree of mixing,momentum transfer, mass transfer, and heat transfer, the morphology ofthe dispersed powders can be tailored. It is important to note that thefocus of the process is on producing a dispersed powder product thatexcels in satisfying the end application requirement and customer needs.In some cases, this may be achieved with uniformly dispersed particlesand in others it may be non-uniformly distributed particles that bestmeet the customer needs.

[0094] After cooling, the nano-dispersed powder is preferably quenchedto lower temperatures at step 116 to minimize and preferably preventagglomeration or grain growth. Suitable quenching methods include, butare not limited to, methods taught in U.S. Pat. No. 5,788,738. It ispreferred that quenching methods be employed which can preventdeposition of the powders on the conveying walls. These methods mayinclude electrostatic means, blanketing with gases, the use of higherflow rates, mechanical means, chemical means, electrochemical means, orsonication/vibration of the walls.

[0095] In one embodiment, the high temperature processing systemincludes instrumentation 112, 114 that can assist in the quality controlof the process by analyzing the quality of the product either betweensteps 116 and 118, or between steps 118 and 120. The data collectedafter analysis of the product can provide information on how to adjustthe process variables to adjust the quality of the product.

[0096] It is preferred that the high temperature processing zone 106 isoperated to produce fine powders 120 (FIG. 3), preferably submicronpowders, and most preferably nanopowders. The gaseous products from theprocess may be monitored for composition, temperature and othervariables to ensure quality at 112 (FIG. 3). The gaseous products may berecycled to be used in process 108 (FIG. 3), or used as a valuable rawmaterial when dispersed powders 120 have been formed. Followingquenching step 116 (FIG. 3) the nano-dispersed powders are cooledfurther at step 118 and then harvested at step 120.

[0097] The product nano-dispersed powders 120 may be collected by anymethod. Suitable collection means include, but are not limited to, bagfiltration, electrostatic separation, membrane filtration, cyclones,impact filtration, centrifugation, hydrocyclones, thermophoresis,magnetic separation, and combinations thereof.

[0098]FIG. 5 shows an alternate embodiment for producing dispersedparticles according to this invention. The embodiment shown in FIG. 5begins with nano-scale powders 200 produced by any technique. Thesenanoscale powders 200 are mixed with desired coarser carrier particles202 into a slurry precursor 204. The slurry precursor 204 is mixed witha fluid such as a fuel and then used as precursor to make nano-dispersedparticles following steps 204-210 in a manner similar to that describedfor steps 104-112 of FIG. 3.

[0099] Alternatively, precursors may be blended into or emulsified intoa commercially available nanoparticulate sol, such as NALCO® silica solsor NYACOL® alumina sol. This multi-phased feed is then used to makeparticles by the process described by FIG. 5.

[0100]FIG. 6 shows yet another embodiment for producing dispersedparticles according to this invention. In this method, both thenano-scale particles and the carrier particles are formed in-situ duringthe thermal processing step. More specifically, a metal-containingprecursor 300 (containing one or a mixture of metal-containingprecursors) and optional dopants 301 are combined to form a precursorbatch 302. The dopants may be added to modify or enable the performanceof the dispersed powders suitably for a particular application. Suchdopants include, but are not limited to, transition metals, rare earthmetals, alkali metals, alkaline earth metals, semi-metals, andnon-metals. It is preferred that, like other metal precursors,precursors for such dopants are intimately mixed with themetal-containing precursor 300. It is also preferred that dopantprecursors are fluids. The precursor batch is then feed into a hightemperature reactor 306. In one embodiment, one or more synthetic aidssuch as a reactive fluid 308 can be added along with the precursor batch302 as it is being fed into the reactor 306. Examples of synthetic aidsinclude, but are not limited to, oxygen, methane, nitrogen, feed gases,oxidants, or reactants.

[0101] With continued reference to FIG. 6, the precursor batch 302 isthen fed into a thermal reactor 306 where the precursors are partiallytransformed, or preferably completely transformed, into the vapor form.The source of thermal energy in the preferred embodiments is plasmagenerator 305. Plasma gas 307, which may be inert or reactive, issupplied to plasma generator 305. Alternatively, the source of thermalenergy may be internal energy, heat of reaction, conductive, convective,radiative, inductive, microwave, electromagnetic, direct or pulsedelectric arc, laser, nuclear, or combinations thereof, so long as it issufficient to cause the rapid vaporization of the powder suspensionbeing processed.

[0102] The high temperature process 306 results in a vapor comprisingboth fine powders and carrier particles formed in-situ from theprecursors 300. In order to produce both the dispersed and carrierparticles, the thermokinetic conditions and ratio of the precursor tothe synthetic aid are controlled. Alternatively, the precursors can befed at different locations in the reactor to engineer the residence timeexperienced by each feed location. A change in residence time orthermokinetic condition or process variable produces powders ofdifferent characteristics (size, shape, composition, etc.). This methodcan therefore be employed to produce both carrier and attachedparticles. After the thermal processing, this vapor is cooled at step310 to nucleate dispersion of the onto the surface of the carrierparticles. Preferably, the cooling temperature at step 310 is highenough to prevent moisture condensation.

[0103] With continued reference to FIG. 6, after cooling step 310 thenano-dispersed powder is preferably quenched as described above to lowertemperatures at step 316 to prevent agglomeration or grain growth. It ispreferred that quenching methods be employed which can preventdeposition of the powders on the conveying walls. Following quenchingstep 316 the nano-dispersed powders are cooled further at step 318 andthen harvested at step 320. The product of this process is a dispersedpowder, such as nano-scale particles dispersed on larger nano-scaleparticles or nano-scale particles dispersed on sub-micron particles.

[0104] In yet another embodiment (not shown), the nano-dispersed powdersare produced by first combining nano-scale powders produced by anymethod with carrier particles. The relative concentrations of thenano-scale powder and the carrier particles should be substantiallyequivalent to that desired in the final product. The mixture is thenmechanically milled by methods known in the art to produce thenano-dispersed powders. The milling may be done in gas or liquidenvironment. If a liquid environment is employed, the liquid maycomprise acids, alkalis, oxidizers, dispersants, metal containingprecursors, or other suitable constituents.

[0105]FIG. 7 shows an alternative flow diagram of a thermal process forthe synthesis of nano-dispersed powders. In this method, precursors 404such as metal containing emulsions, fluid, or water soluble salt, arecombined with carrier particles 405. Although a single precursor storagetank 404 is shown in FIG. 7, it is to be understood that multipleprecursor tanks may be provided and used with or without premixingmechanisms (not shown) to premix multiple precursors before feeding intoreactor 401.

[0106] In one embodiment, a feed stream of precursor material fromstorage tank 404 and carrier particles 405 is atomized in mixingapparatus 403. Alternatively, a precursor storage 404 may be implementedby suspending the precursor in a gas, preferably in a continuousoperation, using fluidized beds, spouting beds, hoppers, or combinationsthereof, as best suited to the nature of the precursor.

[0107] The resulting suspension is advantageously preheated in a heatexchanger (not shown), preferably with the exhaust heat, and is then fedinto a thermal reactor 401 where the atomized precursors are partiallytransformed, or preferably completely transformed, into the vapor form.The source of thermal energy in the preferred embodiments is plasmagenerator 402 powered by power supply 206. Plasma gas 407, which may beinert or reactive, is supplied to plasma generator 402. Alternatively,the source of thermal energy may be internal energy, heat of reaction,conductive, convective, radiative, inductive, microwave,electromagnetic, direct or pulsed electric arc, laser, nuclear, orcombinations thereof, so long as it is sufficient to cause the rapidvaporization of the precursor being processed. The peak temperature inthe thermal reactor 401 is greater than 1500° C., preferably greaterthan 2500° C., more preferably greater than 3000° C., and mostpreferably greater than 4000° C. Optionally, in order to preventcontamination of the vapor stream caused by partial sublimation orvaporization, the walls of reactor 401 may be pre-coated with the samematerial being processed.

[0108] The vapor next enters an extended reaction zone 411 of thethermal reactor which provides additional residence time as needed tocomplete the processing of the feed material and to provide additionalreaction and forming time for the vapor (if necessary) . As the streamleaves the reactor, it passes through a zone 409 where the thermokineticconditions favor the nucleation of solid powders from the vaporizedprecursor. These conditions are determined by calculating thesupersaturation ratio and critical cluster size required to initiatenucleation. Rapid quenching leads to high supersaturation which givesrise to homogeneous nucleation. The zones 401, 411, and 409 may becombined and integrated in any manner to enhance material, energy,momentum, and/or reaction efficiency.

[0109] As soon as the vapor has begun nucleation, the process stream isquenched in a heat removal apparatus within nucleation zone 409comprising, for example, a converging-diverging nozzle-driven adiabaticexpansion chamber at rates at least exceeding 1,000 K/sec, preferablygreater than 1,000,000 K/sec, or as high as possible. A cooling medium(not shown) may be utilized for the converging-diverging nozzle toprevent contamination of the product and damage to the expansionchamber.

[0110] The quenched gas stream is filtered by appropriate separationequipment in harvesting region 413 to remove the nano-dispersed productfrom the gas stream. As is well understood in the art, the filtrationcan be accomplished by single stage or multistage impingement filters,electrostatic filters, screen filters, fabric filters, cyclones,scrubbers, magnetic filters, or combinations thereof. The filterednano-dispersed product is then harvested from the filter, either inbatch mode or continuously, using screw conveyors or gas-phase solidtransport, and the product stream is conveyed to powder processing orpackaging unit operations (not shown).

[0111] The process is preferably operated at near ambient pressures andmore preferably at pressures that are less than 750 mm Hg absolute (i.e.vacuum) . Such a low pressure can be achieved using any type of vacuumpump, compressor, and more preferably using compressed fluid-basedeductor operating on a venturi principle given the lower cost,simplicity and environmental benefits. Vacuum generating equipment maybe placed at any stage of the overall process. The product stream fromthe vacuum generating equipment may be utilized elsewhere in the processto achieve heat and mass integration and thereby to reduce costs. Forexample, in one embodiment a suspension or dispersion may be prepared ina liquid directly if the liquid were to be utilized as the high pressuredriving fluid for the eductor.

[0112] In an alternate embodiment shown in FIG. 8, rather thanharvesting the nano-dispersed product, the nano-dispersed product isdeposited directly on a substrate 601 to form a coating or film ornear-net shape structural part. In this embodiment, the fluid precursor504 and carrier particles 505 are fed into mixing apparatus 503 and thenfed into a thermal reactor 501 where the atomized precursors arepartially transformed, or preferably completely transformed, into thevapor form.

[0113] The preferred source of thermal energy in the embodimentillustrated in FIG. 8 is plasma generator 502 powered by power supply506. The mixture is thermally heated in reactor 501 to high temperaturesto yield a hot vapor. A substrate 601 having an exposed surface isprovided within or in communication with reaction chamber 501 on, forexample, a thermally controlled substrate holder. The hot vapor is thencontacted with the exposed substrate surface and coats the exposedsurface. The hot vapor may be cooled or quenched before the depositionstep to provide a stream that has fine liquid droplets or hotparticulate matter. The substrate 601 may be cooled or heated using asubstrate thermal control 514 to affect the quality of the coating.

[0114] The substrate 601 may be mounted on a turn-table or drum torotate the substrate 601 parallel, perpendicularly, tangentially (or atany other angle) relative to the gas stream comprising of nanoparticles.The rotation can help achieve different thickness, a conformal form, ora curved form. The substrate 601 to be coated may be continuously fedand removed over rotating cylinders to substrate 601. By controlling thesubstrate feed rate, the coating thickness can be controlled. Suchcoating method can employ suitable in-situ instrumentation to controlthe quality of the coating formed.

[0115] The deposition approach in accordance with the present inventionis different from thermal spray technology currently in used in manyways such as: (a) the feed in conventional methods is a solid micronsized powder in thermal spray processes, whereas in this invention thefeed is a fluid precursor; and (b) the conventional thermal sprayprocess is considered to yield a powder with molten surface which thensticks to the substrate, whereas in this invention, as the hot vaporcools it is anticipated to yield a molten droplet or soft particulatethat forms the coating. The advantage of forming a coating or filmaccording to this invention is the fine to nanoscale microstructure ofthe resultant coating or film.

[0116] Furthermore, it is contemplated that the present invention willyield additional benefits in the ability to easily transport fluidswithin the process, the ability to form coatings, and the ability toform wide range of compositions (oxides, carbides, nitrides, borides,multimetal compositions, composites, etc.) from a limited collection ofprecursors through mixing and other methods as taught herein.

[0117] A coating, film, or component may also be prepared by dispersingthe dispersed nanopowder, followed by applying various known methodssuch as, but not limited to, electrophoretic deposition, magnetophoreticdeposition, spin coating, dip coating, spraying, brushing, screenprinting, ink-jet printing, toner printing, and sintering. Thenanopowders may be thermally treated or reacted to enhance theirelectrical, optical, photonic, catalytic, thermal, magnetic, structural,electronic, emission, processing, or forming properties before such astep.

[0118] The powder may be post-processed to further improve itsperformance or characteristics such as flowability. For example, thepost-processing of the dispersed powder may be include one or more ofthe following steps in any order: air classification, sieving, drying,reduction, chemical reaction with liquid, chemical reaction with gases,humidification, surface treatment, coating, pyrolysis, combustion,casting, dispersion, dissolution, suspension, molding, hipping,pressing, milling, composite forming, coarsening, mixing, agglomeration,de-agglomeration, weighing, and packaging. A non-limiting illustrationof such post-processing would be where the dispersed powder aredissolved in a media selected such that the carrier particle dissolvesin the media while the attached particles do not dissolve in the media.This post-processing can produce hollow nanostructured or sub-micronparticles. Similarly, if the dispersed particles comprise of a polymericcarrier powders and the attached particles are ceramic, pyrolysis orcombustion can also be utilized to make hollow particles. Such hollowparticles are anticipated to have unusual properties such as lowereffective density, low effective dielectric constant, lower effectivethermal conductivity.

[0119] Uses

[0120] Dispersed powders have numerous applications in industries suchas, but not limited to, catalysis, biomedical, pharmaceuticals, sensor,electronic, telecom, optics, electrical, photonic, thermal, piezo,magnetic and electrochemical products.

[0121] Biomedical implants and surgical tools can benefit from dispersedpowders. It is expected that nano-dispersed powders can enable implantswith modulus and other properties that match the part being replaced.The match is expected to be within 10% of the target properties. Thesurgical tools produced using nano-dispersed powders are expected tooffer strength that is at least 10% higher than that achieved usingpowders without nano-dispersion.

[0122] Powdered marker, drug carriers and inhalation particulates thatreduce side effects can benefit from nano-dispersed powders. Forinhalation product applications, carrier particles with a size range of500 nm to 50 microns are preferred, and carrier particles with ageometric diameter of 1-50 μm and an aerodynamic diameter of 1-10 μm aremost preferred. The nanoscale dispersed particle can be a drug or acarrier of the drug. The carrier particle can be engineered to favorprolonged release. For injectable product applications, carrierparticles with a size range of 100 nm to 25 microns are preferred, andcarrier particles with a geometric diameter of 0.1-5 μm and anaerodynamic diameter of 0.1-1 μm are most preferred. The nanoscaledispersed particles can be markers, tracers, drug vehicles or targetcarriers.

[0123] Another category of application of nano-dispersed powders isphosphors. Phosphors emit light when exposed to radiation. Not-limitingillustrations of phosphors include Zn₂SiO₄:Mn, ZnS:Ag, ZnO:Zn,CaSiO₃:Mn, Y₃Al₅O₁₂:Ce, Y₂O₃:Eu, Y₂SiO₅:Ce, Y₃(Al,Ga)₅O₁₂:Tb,BaO.6Al₂O₃:Mn, BaMg₂Al₁₆O₂₇:Eu, CsI:Na, and CaS:Ce,Sm. It is expectedthat the methods of manufacture and other teachings of this inventioncan be applied wherein the major phase of the phosphor is the carrierparticle and the minor phase is the nano-dispersed particle. As anon-limiting example, for Y₃Al₅O₁₂:Ce, Y₃Al₅O₁₂ can be the carrierparticle while Ce is the nano-dispersed phase on the surface of thecarrier. For phosphor product applications, carrier particles with asize range of 50 nm to 25 microns are preferred, and carrier particleswith a geometric diameter of 0.5-10 microns are preferred. The dispersedparticles with a size range of 1 nm to 0.5 microns are preferred, anddispersed particles with a geometric diameter of 1-100 nanometers arepreferred. It is anticipated that the light emitting efficiency ofnano-dispersed phosphor powders will be higher by 5% or more thanphosphor powder of equivalent composition that is not dispersed. Thescope of this invention includes Stoke and anti-Stoke phosphors.Nano-dispersed phosphor powders can be used in lamps, cathode ray tubes,field emission displays, plasma display panels, scintillators, X-raydetectors, IR detectors, UV detectors and laser detectors.Nano-dispersed phosphor powders can also be used in printing inks, ordispersed in plastics to prevent forgery and counterfeiting of currency,original works of art, passports, credit cards, bank checks, and otherdocuments or products. The nano-dispersed powders can also be used toprepare optical networking components such as detectors, emitters,photodiodes, and phototransistors.

[0124] Another broad use of nano-dispersed powders is in electrical andelectronic components such as capacitors, inductors, resistors,thermistors, sensors and varistors. Nano-dispersed particles canincrease the reliability of these components by 10% or more when used aselectroceramic dopants. Furthermore, nano-dispersed particles can enableminiaturization of these components by enabling ceramic layerthicknesses below 500 nm and electrode layer thicknesses below 400 nm.

[0125] Electrochemical capacitors prepared from nano-dispersed powdersare expected to have charge densities that are 10% higher than thoseprepared from non-dispersed powders of equivalent composition. Theelectrochemical capacitors are also expected to offer high volumetricefficiencies, and longer mean times between failures. Batteries preparedfrom nano-dispersed powders can offer power densities that are 5% higherthan those prepared from non-dispersed powders of equivalentcomposition. Chemical sensors prepared from nano-dispersed powder areexpected to offer sensitivities that are at least 10% higher than thoseprepared from non-dispersed powders of equivalent composition.

[0126] A major application area for nano-dispersed powders producedusing the high temperature process of this invention is in chemicalcatalysis. Catalytic materials that are prepared from nano-dispersedpowders are expected to last 10% or more longer and give superior yieldsand selectivity than catalytic materials prepared from non-dispersedpowders of equivalent composition. They are also expected to offer turnover rates that are 5% higher than those prepared from non-dispersedpowders of equivalent composition. For this application, the process ofthis invention for producing nano-dispersed powders can additionallyoffer desirable porosity, structural strength, and uniformity. Examplesof such applications include (a) catalytic transformation of lessvaluable chemicals and material feed stocks into more valuable chemicalsand materials and (b) catalytic transformation of more hazardouschemicals and materials into less hazardous or non-hazardous forms ofsubstances.

[0127] Other applications of nano-dispersed powders include (a) fillersfor polymers, ceramics, and metal matrix composites and (b) dopants forelectronic, magnetic, thermal, piezo, electrical, tooling, structural,inks, paints, and topical health products.

[0128] Magnetic devices prepared from dispersed powders are expected tooffer superior magnetic performance. In general, nano-dispersed powdersoffer a means of improving the value-added performance of existingproducts that are produced from non-dispersed powders.

[0129] In some applications where material cost is a critical parameter,affordability can be achieved by combining low cost carrier powders withhighly functional but somewhat more expensive attached nanoparticlesthereby yielding more affordable yet high performance nano-dispersedpowders on a per unit weight basis. As an added benefit, improvedability to process micron size carrier powders can accelerate theadoption of nano-dispersed powders in commerce.

[0130] Other embodiments of the invention will be apparent to thoseskilled in the art from a consideration of the specification or practiceof the invention disclosed herein. It is intended that the specificationand examples be considered as exemplary only, with the true scope andspirit of the invention being indicated by the following claims.

We claim:
 1. A method for producing a dispersed powder comprising nano-sized particles dispersed on and attached to the surface of carrier particles, the method comprising: providing a slurry precursor comprising a mixture of a metal-containing precursor and carrier particles; heating the slurry precursor to a temperature greater than 3000° C., wherein the slurry precursor is converted to the vapor phase; and cooling the vapor phase to produce the dispersed powder.
 2. The method of claim 1, where the temperature is greater than 4000° C.
 3. The method of claim 1, wherein the carrier particle comprises a sub-micron powder.
 4. The method of claim 1, wherein the carrier particle comprises a nanoscale powder.
 5. The method of claim 1, wherein the metal-containing precursor is selected from the group consisting of oxides, carbides, nitrides, borides, metals, and alloys.
 6. The method of claim 1, wherein the metal-containing precursor is of multi-metal composition.
 7. The method of claim 1, wherein the metal-containing precursor comprises a non-stoichiometric ceramic composition.
 8. The method of claim 1, wherein the metal-containing precursor comprises a mixture of at least two different metal-containing precursors.
 9. The method of claim 1, further comprising quenching the dispersed powder.
 10. The method of claim 1, further comprising adding a reactive fluid to said slurry precursor prior to completion of said heating step.
 11. A method for producing a dispersed powder comprising nano-sized particles dispersed on and attached to the surface of carrier particles, the method comprising: combining nano-scale powders and carrier particles to form a slurry precursor; heating the slurry precursor to a temperature greater than 3000° C., wherein the slurry precursor is converted to the vapor phase; and cooling the vapor phase to produce the dispersed powder.
 12. A method for producing a dispersed powder comprising nano-sized particles dispersed on and attached to the surface of carrier particles, the method comprising: providing a slurry precursor comprising a metal-containing precursor; heating the slurry precursor to a temperature greater than 3000° C., wherein the slurry precursor is converted to the vapor phase comprising nano-scale particles and carrier particles; and cooling the vapor phase to produce the dispersed powder.
 13. A method for producing a dispersed powder comprising nano-sized particles dispersed on and attached to the surface of carrier particles, the method comprising: providing a slurry precursor comprising a mixture of a metal-containing precursor and carrier particles; and mechanically milling said mixture to produce said dispersed powder.
 14. A dispersed powder comprising: a sub-micron carrier particle having a first composition; and nano-scale particles of a second composition that are dispersed on and attached to the surface of the carrier particle in a mechanically stable state, wherein the attached particles are smaller than the carrier particle and wherein at least two neighboring attached particles on the surface of said carrier particle do not touch each other at 300 Kelvin.
 15. The dispersed powder of claim 14, wherein the distance between the at least two neighboring attached particles on the surface of the carrier that do not touch each other is at least 2 Angstroms.
 16. The dispersed powder of claim 15, wherein said distance is greater than 5 Angstroms.
 17. The dispersed powder of claim 15, wherein said distance is greater than 10 Angstroms.
 18. The dispersed powder of claim 15, wherein said distance is greater than 50 Angstroms.
 19. The dispersed powder of claim 14, wherein the ratio of the average diameter of the carrier particles and the average diameter of the attached particles is greater than or equal to
 2. 20. The dispersed powder of claim 19, wherein said ratio is greater than
 10. 21. The dispersed powder of claim 19, wherein said ratio is greater than
 25. 22. The dispersed powder of claim 19, wherein said ratio is greater than
 100. 23. The dispersed powder of claim 14, wherein the surfaces of the attached particle and carrier particle interact physically, chemically, electrochemically.
 24. The dispersed powder of claim 14, wherein the carrier particle is nanoscale particle.
 25. The dispersed powder of claim 14, wherein the composition of the attached particle is selected from the group consisting of oxides, carbides, nitrides, borides, metals, and alloys.
 26. The dispersed powder of claim 14, wherein the attached particle is a multi-metal composition.
 27. The dispersed powder of claim 14, wherein the attached particle is a non-stoichiometric ceramic composition.
 28. The dispersed powder of claim 14, wherein the composition of said nano-sized particles is the same as the composition of said carrier particles.
 29. The dispersed powder of claim 14, wherein the composition of said nano-sized particles is different than the composition of said carrier particles.
 30. A product containing a dispersed powder of claim
 14. 31. The dispersed powder of claim 14, wherein the dispersed powder has been post-processed. 